Lost tail lights and dash lights on my current trip. Any ideas? 2007 FG

[gait]

I wish I'd known that's where the dome light is powered from a couple of years ago. I'm still chasing shorts from near fire. The fuse in the under dash fuse box melted and didn't blow. So the wire melted and took a few others with it. All with ignition off = near fire. Took out lots of the control wiring so I performed a few bypass operations to get things like aircon and windows and wipers and headlights working. The power circuits are generally easier than the control circuits but in general the Canter electrics are enormously (and unnecessarily IMHO) over complicated.

 

[dtruzinski]

For such a simple circuit, I am sure having huge challenges finding the root cause. Maybe I am doing something wrong. I am testing by taking a volt meter across the fuse connection. If the problem is solved, my meter should read 0 volts, but while I have a wire or switch going to ground I am reading North of 12v. Does that sound like a valid test? I have given up for the night...it's cold here in Montana. Started troubleshooting at 15F and finished at a near high of 25...plastic panels are hard to get off in those conditions. Thanks again for your help...it's research time.

 

[gait]

hard to concentrate in the cold .... but at least its easier to put clothes on to get warm, there's a limit to taking them off to get cool!

sounds valid to me. Red meter wire on battery side of fuse, no fuse in place, black wire for meter on other side. If 12v then black side is at ground.

Be a little wary though. The lights have fairly low resistance. If its a dead short the volts between red side of fuse and ground will be the same as from red side of fuse to black side of fuse.

Similar test is to check the resistance between black side of fuse and ground. It should not be zero.

Then pull out the rear light relay and test across the fuse again. That will confirm that the short is between relay and rear lights.

After that I'd look for the connectors close to the rear lights and separate them. Then test at the fuse again. If the result changes the problem is between the connector and lights, else between connector and relay.

After each test retreat indoors to warm up.

 

[dtruzinski]

@gait - I have now named this process "The Hunt for GW" (like the Hunt for Red October, but no subs).

I have made progress. I found the junction box for cab vs chassis wiring and then located the connector that contained the two wires from the High Current Fuse box for the tail lights. One is red-blue and is direct to the fuse in the High Current Fuse box. The other is Green White (GW) and on the tail light relay. When I separate the chassis from the cab and number the relay, presto...tail light ablaze and the fuse holds. So I check the cab side of the GW wire and sure enough it goes to ground (somewhere in the cab). Problem is that damn GW wire is used just about everywhere according to the diagrams. At least now I can warm up the cab and troubleshoot whist inside. I am learning a lot more about reading wiring diagrams than I ever wanted to know and I finally grasp control vs power circuits.

 

[gait]

well done. I don't know about you but fault finding those maizes can be quite hard as not only is it a maize the results of tests can often seem to conflict - there's that horrible thought of going mad. Trying to do it over a forum can be diabolical.

Lights on without fuse blowing is fairly conclusive though. Yeah!

Good luck with following the GW wire. I have no idea what is hung off it. As well as the distinction between control and power circuits there's a distinction between wiring and equipment problems. My feeling (with absolutely no evidence and allow me to be wrong) is that you have a wiring problem. Looking for chafed or melted wire or melted connector. Different to a problem inside some equipment, like a fan motor stalled or something else not right.

Having drawn the distinction between wiring and equipment the process of elimination continues but the emphasis on following the wires. Starting at the other end, by temporarily disconnecting equipment close to the equipment may not eliminate the problem (if it does that's a bonus and makes life easy) but it does help confirm a wiring problem and isolate it to the main loom.

In my case I had to cut the equivalent of the GW wire at both (all) ends and rewire with by-passes as I haven't physically found the short yet. I just know roughly which section of the wire its in.

Too early for you to contemplate that. Needs a bit more searching and diagnosis.

 

[dtruzinski]

VICTORY! and it only took 3 full days

On the drivers side of the dash near the brake fluid container there is a Joint of the Main Harness Connector J10. It is labeled "Optional Connector". It had that dreaded GW wire, so I disconnected it and viola, no short on the GW wire. My truck was previously a wild land fire truck and I suspect someone tapped into that circuit for PA, lights and sirens...who knows. This has been a real lesson in chasing wiring problems.

Btw...how did I find that connector? I knew that the GW wire in the cab was shorting to ground somewhere, so I found the Joint Connector J/C3 with this wire. I tested the circuit and it showed a ground fault. Now I was able to isolate the fault; it had to be between the cab connector and that J/C3 connector. The diagram for the J/C3 connector mentioned circuit IL01J. and pointed to Index Number 110. On Index 110, the GW wire on circuit IL01J connected to four new Index Numbers: 320 for headlamps, 348 for rheostat, 349 for ID lamp and clearance markers and 115 for optional connector. The first one I checked was the Optional Connector and presto all was resolved. One day I will dig in and find where it was grounding. In the meantime, I am going to thaw out.

If you run into a Fuso wiring problem, I would he happy to walk you through what I have learned. My gem of knowledge for the day is this:when reading a Fuso wiring diagram the arrows do not, let me repeat "do not" have anything to do with electrical flow. They indicate a junction of two wires! Second gem of the day...when chasing a fault, make sure to look at the connector diagrams in your repair manual. You save a lot of time guessing when you can look for a specific connector. And of course the age old adage RTFM (read the fine manual) for the electrical portion will pay huge dividends.

 

[dtruzinski]

well done. I don't know about you but fault finding those maizes can be quite hard as not only is it a maize the results of tests can often seem to conflict - there's that horrible thought of going mad. Trying to do it over a forum can be diabolical.

Lights on without fuse blowing is fairly conclusive though. Yeah!

Good luck with following the GW wire. I have no idea what is hung off it. As well as the distinction between control and power circuits there's a distinction between wiring and equipment problems. My feeling (with absolutely no evidence and allow me to be wrong) is that you have a wiring problem. Looking for chafed or melted wire or melted connector. Different to a problem inside some equipment, like a fan motor stalled or something else not right.

Having drawn the distinction between wiring and equipment the process of elimination continues but the emphasis on following the wires. Starting at the other end, by temporarily disconnecting equipment close to the equipment may not eliminate the problem (if it does that's a bonus and makes life easy) but it does help confirm a wiring problem and isolate it to the main loom.

In my case I had to cut the equivalent of the GW wire at both (all) ends and rewire with by-passes as I haven't physically found the short yet. I just know roughly which section of the wire its in.

Too early for you to contemplate that. Needs a bit more searching and diagnosis.

Thanks for your help and encouragement...this was quite a journey!

 

[dtruzinski]

Joint Connectors j/c 1-3 and Optional connector PICS for your reference (and mine)

On the passenger side you can see the three big joint connectors. Basically they take a hot from one circuit and spread it to one or more other circuits. I know J/C3 is the one with the brown and gray connector bars; I suspect the all green one is J/C3 and J/C1 is the one on the left.


On the drivers side the Optional Connector is tucked up under the dash. It is the large white connector that is separated.

 

[gait]

well done again, and thanks.

The manual, particularly the electrical bit, is well indexed once got used to. Just takes a bit of time...